3 pn-CCD and MOS-CCD images

Images in celestial coordinates with a pixel size of 2 arcsec have been accumulated in the 0.5-7 keV band for all three detectors. Figure 1 shows a comparison of the image from the PN (left) and the MOS1+MOS2 camera (right). Albeit the variation in pointing direction between different revolutions, the shadows of the inter-CCD gaps appear in the images due to an interference between the variations in pointing direction and roll angles. An exposure map was calculated for the combination of pn-CCD plus MOS1 and MOS2 cameras (Fig. 2a).

The brighter X-ray sources in the images have been already optically identified from the ROSAT data (Schmidt et al. 1998; Lehmann et al. 2000,2001). X-ray sources identified with point-like optical objects (i.e. AGN or stars) have been used to check and correct the astrometry of the images. Positions of the brighter X-ray sources were centroided by an elliptical 2D-Gaussian fit. The FWHM of the point spread function in the center of the field was found to be 8.9 and 7.7 arcsec for the PN and MOS images, respectively. The X-ray source centroid sky coordinates calculated from the WCS keywords were offset by 5 $\hbox{$^{\prime\prime}$ }$-25 $\hbox{$^{\prime\prime}$ }$ from the known optical counterparts. Thus a transversal shift and a rotation angle were fit for each dataset. For the PN, satisfactory fits were achieved by fixing the scale factor of the X-ray image to 1.0, leading to residual systematic errors to $\sim$1 $\hbox{$^{\prime\prime}$ }$. For the MOS's, introducing different scaling factors along the X- and Y-axes, in addition to the transversal shift and rotation, improved the fits significantly. This reflects the fact that the geometrical layout of the CCD chips in the MOS cameras had not yet been satisfactorily established. The Lockman Hole observations can be used to improve the knowledge of the layout, which then will be incorporated into future pipeline processings. For our current analysis, we use these ad-hoc corrections, which lead to residual systematic position errors of 1-3 $\hbox{$^{\prime\prime}$ }$.

Figure 1: X-ray images of the Lockman Hole obtained with the pn-CCD (left) and MOS 1+2 (right) cameras. The images have been summed up over all XMM-revolutions for a total exposure of about 100 ksec and are accumulated in the 0.5-7 keV band. Both images are 30 $\times$ 30 arcmin across. North is up and East is left

Figure 2: a) (left) Combined exposure map for the PN and MOS images in Fig. 1. b) X-ray ``real-colour'' image of the combined and exposure corrected PN and MOS images. The colour refers to different X-ray energy bands: red, green and blue correspond to the 0.5-2, 2-4.5 and 4.5-10 keV range, respectively

Figure 3: Cumulative source counts N(S) in the 0.5-2 keV (left), 2-10 keV (middle) and 5-10 keV band (right). The XMM data are shown as thick solid line. In the 0.5-2 keV band the data is compared with the ROSAT source counts and fluctuation analysis (Hasinger et al. 1998a) and with the Chandra source counts (dashed line) of Giacconi et al. (2000). In the 2-10 keV band the solid line at bright fluxes refers to the ASCA counts by Cagnoni et al. (1998), while the dashed line at faint fluxes again refer to the Chandra counts and the dotted region refers to the BeppoSAX fluctuation analysis by Perri & Giommi (2000). In the 5-10 keV band the XMM counts are compared to the BeppoSAX log(N)-log(S) by Fiore et al. (1999) and to a prediction based on the most recent background synthesis model by Gilli et al. (1999)